When children are diagnosed with cancer, their entire family is affected. As part of the family system, healthy siblings of children with cancer may witness their brother or sister in physical and emotional pain, experience sudden and extended separations from him or her, and worry that he or she will die. Additionally, these siblings may be separated from at least one of their parents for extended periods, have their daily routines disrupted, and need to negotiate changes in family roles and responsibilities due to cancer and its treatment. Given the level of disruption that childhood cancer causes for families, it is not surprising that siblings of children with cancer have been found to display anxiety, depression, and posttraumatic stress. At the same time, however, some siblings report positive outcomes of cancer such as enhanced empathy and maturity. Little is known about what distinguishes siblings who thrive after cancer from those that have difficulties. The few research studies available suggest siblings' beliefs about the cancer experience and their perceptions about the effects of cancer on their family system influence their emotional and behavioral reactions to cancer. The goal of the proposed study is to create a reliable and valid method for assessing the cancer-related beliefs of siblings that are associated with their adjustment. The Specific Aims of the project are: 1) Create a measure of the cancer-related beliefs held by siblings of children with cancer based upon focus groups with siblings, a review of the literature, and input from experts working with families of children with cancer; 2) Refine the measure, determine its structure, and assess its reliability (i.e., internal consistency, test-retest reliability) after administering it to 150 siblings of children with cancer; 3) Evaluate the validity of the refined measure against a currently used measure of siblings' perceptions of cancer, measures of psychosocial adjustment, family functioning, and dispositional characteristics; and 4) Explore variation in the measure as a function of developmental stage. Unlike current measures for assessing sibling's beliefs, the Sibling Illness Belief Inventory (SIBI) is innovative in that it will include a broad range of beliefs (i.e., both growth enhancing and growth-inhibiting beliefs) and serve as a first step in a program of research aimed at creating an intervention that targets cancer-related beliefs of siblings to improve their adjustment to cancer.